China launched one of the most ambitious and controversial torch relays in the history of the Olympics yesterday with a tightly restricted ceremony in the heart of Beijing.

After anti-government protests this month in Tibet, three other provinces and at least four countries, security was so tight at the venue that the vast concrete expanse of Tiananmen Square, which once staged rallies of more than a million people, was empty of all but 5,000 vetted guests.

Paramilitary police were stationed on every overpass and slip road along the route of the torch. Security personnel were placed on nearby buildings, two stations were shut and Tiananmen was closed down the night before, causing long traffic tailbacks.

The hosts, who have spent billions of dollars preparing Beijing for the games, said the arrival of the torch was a momentous event. "The burning Olympic flame will spread the message of peace and friendship and unite all people under one world, one dream," said Liu Qi, president of the Beijing Olympic organising committee, at the event.

The relay will be the longest ever, passing through 19 nations and almost every province in China on a 130-day journey that includes an ascent of Mount Everest.

Organisers hope the route will highlight China's growing ambitions, economic development and openness to the outside world.

But it looks set to be dogged by protests at several spots on a range of issues, including human rights abuses, censorship, persecution of religious groups and support for Sudan.

The torch arrived on a chartered China Airlines flight from Greece - the scene of demonstrations by Tibetan supporters as it left yesterday and by free-speech campaigners when it was lit last week.

Its welcome was warmer in Beijing. Hundreds of people waved Chinese and Olympic flags as the plane arrived at Beijing international airport.

At a nationally broadcast ceremony in Tiananmen Square the president, Hu Jintao, relit the torch and passed the flame to Olympic champion hurdler Liu Xiang, as coloured balloons rose up into the clear blue sky, glittering confetti cascaded down and drummers decked out in red and yellow pounded out a beat.

The flame heads off to Almaty, Kazakhstan, today on an 85,000-mile journey around the globe, before returning to China on May 3.

It will be carried by a record number of torch bearers and - given the number of flights involved - will quite possibly also have a bigger eco-footprint than any previous relay.

The main focus for protesters is Tibet, which was rocked by riots on March 14. The unrest has since spread to three neighbouring provinces. China blames the Dalai Lama for orchestrating the disturbances to upset the country's Olympic preparations.

At the weekend, the state-run Xinhua news agency said a monk had confessed that the "Dalai Clique" had instructed him to hand out leaflets encouraging people to protest. The agency did not provide the name of the monk, nor the nature of the demonstration that might have been called for. Human rights groups say many confessions in China are extracted under torture.

The Dalai Lama has denied instigating the unrest, which China says led to the deaths of at least 18 civilians and a police officer. Tibetan groups claim the death toll is far higher and includes many protesters shot or beaten by police.

Despite the fierce criticism of the Dalai Lama in the state media, the Chinese prime minister, Wen Jiabao, said at the weekend that the door was still open to talks with Tibet's spiritual leader.